I. Field of the Invention
The present invention relates generally to portable, motorized concrete vibrator tools. More particularly, my new invention relates to a portable, motor-driven, pendulous vibrator system for consolidating freshly poured concrete. Prior art relative to my new system may be found in Class 366, subclasses 117, 120-123, 128, and 129.
II. Description of the Prior Art
It is well settled that freshly poured concrete must be properly vibrated after placement for adequate consolidation. Properly-applied vibration settles and densifies the concrete mass, and eliminates air voids. Preexisting concrete vibrating equipment ranges from extremely large, vibrating screed units that ride upon forms while traversing freshly poured concrete, to smaller, portable units which can be handled by a single workman. The smaller units may include motor-driven tools associated with a portable system. These enable the contractor to properly densify smaller-to-medium pours that are difficult to reach with large conventional units. Portable vibrator systems enable the operator to easily reach certain locations that are inaccessible to large screeds. Backpack systems readily transport and control a fairly substantial vibration unit that is capable of densifying several yards of green concrete.
Some jobs are so small that even a backpack system amounts to overkill. Miniature hand-held units, for example, may be capable of properly handling smaller pours in the order of a couple of yards or less. Providing their horsepower ratings and vibrational output are satisfactory, they may be able to properly consolidate smaller pours within the curing time frame associated with quick setting cement.
U.S. Pat. Nos. 4,483,070, 4,644,654, 4,662,551, 4,658,778, 2,519,939, 2,792,670, 1,981,076, and Great Britain Pat. No. 768,419 all show various forms of motorized tools that are transported upon a backpack worn by the user.
U.S. Pat. Nos. 2,167,987, 2,603,459, 2,597,505, 3,608,867, 3,395,894, and Reissue No. 21,684, show vibrating heads suitable for concrete work that are activated by motor-driven cables to produce vibration.
U.S. Pat. Nos. 2,430,817, 2,492,431, 3,042,386, 3,180,625, and 3,188,054 all depict hand-held, portable vibrating machines for treating concrete that have remote vibrator heads adapted to be immersed in freshly poured cement.
Known portable vibrator systems employ a two-cycle engine that must run at relatively high RPM. The engine connects via a flex-shaft cable to an eccentric vibrator unit that is immersed within the concrete. As the engine rotates the flex-shaft through the cable, vibration created by the eccentric vibrator is transmitted to the concrete. During operation, heat builds up and the flex-shaft and casing components expand. Expansion causes "preloading," in that the flex-shaft is pressured axially, stressing mechanical parts. Also, the flex shaft itself is stressed radially, causing excessive rubbing against the outer casing. This stress and rubbing weakens the parts, and the excessive friction generates heat that burns the hands of the operator.
Two-cycle engines are normally used to reach the desired RPM ranges for proper vibration frequencies. These engines normally run very hot, partly because they run at relatively high RPM's. With known eccentric vibrators, two-cycle engines lack the proper torque at low RPM's. Additionally, two-cycle motors require a proper mixture of gasoline and oil for optimum operation. However, in the field, the reality is that improper oil-gas mixtures are often used. Further, operators often over-rev the engines to obtain the relatively high rotational speed required by traditional flex-shaft eccentric vibrators to produce high frequency vibration. Speed increases can aggravate the heat problem. As a result, two-cycle systems can be inefficient, cumbersome, and unreliable.
Nevertheless, two-cycle engines have traditionally been preferred because they generally produce higher RPM's. High speed is necessary for traditional flex-shaft eccentric vibrators. Further, two-cycle engines are usually smaller and significantly lighter than conventional four cycle engines. These reasons dictate their common use in portable vibrating systems and in a variety of portable, hand-held appliances such as rotary grass trimmers.
Common knowledge might suggest the use of four cycle engines. They may be heavier and slower, but they are inherently more reliable and they are comparatively maintenance free. However, four-cycle engines are seldom used with conventional portable vibrators, since smaller, lightweight units are thought by many to be incapable of the required horsepower and rotational speed. Gear systems have been tiled for increasing speed with four-cycle systems, but the resultant size and weight render such designs unfit for one-man, portable systems.
Pendulous vibrators are known in the art. They are virtually maintenance free when compared with typical eccentric vibrators. Pendulous vibrators produce high frequency vibration with a relatively low RPM input. They effectively multiply the primary input speed of the drive cable system three to five times. However, they require more torque than typical, flex-shaft eccentric vibrators. In the past, pendulous vibrators I have tested overly stressed two-cycle drive systems, causing premature bearing failure from the stress of heat and unbalanced loads. Moreover, the internal construction of the pendulous vibrating head used in previous designs cannot withstand the high speed of two-cycle motors combined with the lightweight design needed in a truly portable, hand-held design.
For small, portable systems it would seem desirable to combine a two cycle engine with a pendulous vibrator. An ideal portable system should meet a number of requirements. First, the system must enable the user to safely and comfortably transport the load with his hands without unbalancing him and causing him to fall. Operator maneuverability must be enhanced. Weight must be minimized, and it must be distributed relatively evenly to preserve operator mobility and balance. Mechanical parts should be flushly and compactly mounted- they must not obstruct or contact the operator. The unit must be stable, even when the engine is running wide open, so that applicator dexterity is only minimally compromised. Vibration and heat must be isolated from the user if possible. Most importantly, the reliability of the vibrator head must be preserved. For high-speed operation, particularly with two-cycle drive motors, special design precautions must be taken within the coupling apparatus controlling the weight inside the vibrator head.